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On adhesion of work material in metal forming
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
2008 (English)In: International journal of microstructure and materials properties, ISSN 1741-8410, Vol. 3, no 2-3, 401-412 p.Article in journal (Refereed) Published
Abstract [en]

The transfer of work material to the tool surface limits the tool life in many forming operations. Using a dedicated load-scanning test equipment with crossed-cylinder geometry, dry forming of austenitic stainless steel was simulated by provoking adhesion to the TiN-coated tool specimen. High-resolution electron microscopy combined with analytical techniques was used to examine the interface between tool and work material. The decisive mechanism for adhesion and transfer of steel to the TiN surface is suggested. The oxide layer on the steel surface, especially the Fe-oxide, initiates the metal transfer. The interfacial oxide acts as a glue between stainless steel and TiN and increases the adhesive forces. Obviously, the adhesion and internal strength of the oxide layer is far stronger than anticipated. It may even be stronger than the bonding to the austenitic steel itself. A consequence of these findings is that the development of galling resistance-forming tool materials and coatings for austenitic stainless steels should not only aim to improve the bulk tool material, but also to reduce the adhesion strength between the tool surface and the oxide layer on the work material.

Place, publisher, year, edition, pages
2008. Vol. 3, no 2-3, 401-412 p.
Keyword [en]
metal forming, adhesion, galling, stainless steel, TiN coating, transmission electron microscopy, TEM, focused ion beam, FIB, dry forming, metal transfer, interfacial oxide, austenitic steel
National Category
Engineering and Technology
URN: urn:nbn:se:uu:diva-96667DOI: 10.1504/IJMMP.2008.018744OAI: oai:DiVA.org:uu-96667DiVA: diva2:171316
Available from: 2008-01-24 Created: 2008-01-24 Last updated: 2016-04-13Bibliographically approved
In thesis
1. On Adhesion and Galling in Metal Forming
Open this publication in new window or tab >>On Adhesion and Galling in Metal Forming
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Metal forming is widely used in the industry to produce cans, tubes, car chassis, rods, wires etc. Forming certain materials such as stainless steel, aluminium and titanium, is often difficult, and problems associated with transfer of work material to the tool material are frequent. Transferred material may scratch and deform the following manufactured pieces, a phenomenon named galling. Lubricants can, to some degree, solve these problems. However, many forming oils are hazardous to the environment, and therefore it is highly desirable to replace them or get rid of them.

This thesis investigates the nature of the galling phenomenon and tries to explain under which conditions such problems arise. Dry sliding tests have been performed in a dedicated load-scanner equipment. Difficult work materials have been tested against tool materials under various conditions and the samples have then been studied by advanced analytical techniques, such as ESCA and TEM, to study the detailed tribological mechanisms occurring in the contact between work and tool material.

The general assumption is that material transfer only occurs when there is metal to metal contact. In this work it has been found that, for stainless steel, the oxide plays a very important role for the sticky behaviour of stainless steel, and that metal to metal contact is not a necessary condition for galling.

Several PVD-coated tool materials have been tested and it was found that vanadium nitride coatings can be tuned regarding their chemical composition, to be more galling resistant than conventional coatings.

The surface roughness of the tool material is very strongly coupled to the tools ability to resist galling. The smoother the tool surface, the less risk of material transfer and galling.

Some work materials, like aluminium and titanium, transfer to even the smoothest tool materials. A proposed explanation for this is that their oxides are much harder than the bulk material and the tool material matrix. When deforming the work material, the oxide will fracture into small hard scales, which can indent the tool material. Indented hard scales will then contribute to material transfer of more work material to the tool.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 52 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 388
Engineering physics, adhesion, galling, dry sliding, stainless steel, vanadium nitride, metal forming, Teknisk fysik
urn:nbn:se:uu:diva-8417 (URN)978-91-554-7072-2 (ISBN)
Public defence
2008-02-15, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00
Available from: 2008-01-24 Created: 2008-01-24Bibliographically approved

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